The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Engines such as diesel engines produce particulate matter (PM) that is filtered from exhaust gas by a PM filter, such as a wall-flow PM filter. The PM filter is disposed in an exhaust system of the engine. The PM filter reduces emission of PM that is generated during combustion.
Over time, the PM filter becomes full. During regeneration, the PM may be burned within the PM filter. Regeneration may involve heating the PM filter to a combustion temperature of the PM. There are various ways to perform regeneration including modifying engine management, using a fuel burner, using a catalytic oxidizer to increase the exhaust temperature with after injection of fuel, using resistive heating coils, and/or using microwave energy. The resistive heating coils are typically arranged in contact with the PM filter to allow heating by both conduction and convection.
Regeneration may be performed using an exhaust heating technique or using an electrical heating technique. An exhaust heating technique refers to the heating of an exhaust gas, for example, by post injection of fuel. During a combustion cycle of an engine, an air/fuel mixture is compressed and ignited within a cylinder of the engine. For robustness and to facilitate regeneration, fuel may be injected into the cylinder during the combustion cycle and after ignition of the air/fuel mixture or into the exhaust stream. The fuel may in addition to or alternatively be injected into the exhaust stream or exhaust system. When introduced during or after ignition and/or exhaust strokes of the combustion cycle, the injected fuel, referred to as post-injected (PI) fuel, mixes with the exhaust gas and is oxidized by an oxidation catalyst disposed in the exhaust system. The heat released from the oxidation reaction in the catalyst increases the temperature of the exhaust system, which facilitates the ignition of the particulates in the PM filter.
The electrical heating technique refers to the electrical heating of an exhaust gas entering a PM filter. One or more electrical coils may be disposed upstream from the PM filter and may be activated to heat the exhaust gas. This provides a quick heating and light off of the PM.
PM reduction systems that use fuel tend to decrease fuel economy. For example, many fuel-based PM reduction systems decrease fuel economy by 5%. To improve fuel economy, electrically heated PM reduction systems are used. When electrically heated PM reduction systems are used in combination with fuel-based PM reduction systems, expansion and compression forces can occur within the PM filter. The expansion and compression forces are due to temperature differentials between, for example, an electrically heated zone(s) and a non-electrically heated area(s) of the PM filter. The expansion and compression forces cause stress on the PM filter, which can result in fractures, for example, in the corderite substrate of the PM filter.